The present invention relates to optical devices, and, more particularly, to a planar waveguide device formed on a substrate and a fiber attachment for the same.
BACKGROUND OF THE INVENTION
Optical communication systems require different functional components for high efficiency and network flexibility. Optical circuits based on low-loss glass waveguide are the practical and promising approaches to integrate both active and passive devices as a single module for fiber interconnection. Various deposition methods have been developed to deposit the thick glass layer for the application of integrated optics. Those technologies include: (1) thermal oxidation, (2) sputtering, (3) microwave plasma assisted chemical vapor deposition (MPACVD), (4) plasma-enhanced chemical vapor deposition (PECVD), (5) low pressure chemical vapor deposition (LPCVD), (6) flame hydrolysis deposition (FHD) and (7) sol-gel deposition (SGD).
Of the above-described methods, it has been found that Microwave Plasma Assisted Chemical Vapor Deposition (MCPACVD) is particularly advantageous. MPACVD is described for example in U.S. Pat. No. 4,619,680, the teachings of which are incorporated herein by reference. MPACVD is cost efficient and compatible with Si-based microelectronics. Low loss coupling with a single-mode optical fiber can be achieved cheaply with either passive alignment or active alignment. A wide range of low-loss passive components may be produced on a large wafer. Furthermore, hybrid integration techniques allow additional light sources or active components integrated on the same substrate.
Microwave Plasma Assisted Chemical Vapor Deposition (MPACVD) produces superior quality, low birefringence, low-loss, planar waveguides for integrated optical devices. Microwave plasma initiates the chemical vapor of SiCl4, GeCl4 and oxygen. A Ge-doped silica layer is deposited on a silica or silicon substrate with reasonable high growth rate (e.g. 0.4-0.5 xcexcm/min). The resulted refractive index can be varied between 1.46 (i.e. pure silica) to 1.60 (i.e. pure germania). Waveguides can be fabricated with any desired refractive index profile. Standard photolithography defines the waveguide pattern on a mask layer. The core layer is removed by plasma dry etch, preferably an inductively coupled plasma (ICP) etch. Etch rates of 3000-4000 xc3x85/min have been achieved using ICP compared to a typical etch rates of 200-300 xc3x85/min using conventional RIE. A polished fiber end can be epoxied or soldered to the end facet of a waveguide with a very low optical coupling loss. In addition, etching of silicon V-grooves or U-grooves provides a passive fiber alignment capability.